Yep. I’ve lost a lot of hybrids using only passive protection with frost cloth, plastic sheeting, hoop house, water barrels, jugs of water, etc. when it’s polar vortex and below zero all night for several days or even below freezing for a few days with a low of 7 degrees. I do have drop cords going to each tree with small space heaters controlled by thermo cubes, and I am ready to cover even hybrids if we go into low teens or single digits. I’m just tired of loosing trees and waiting for them to come back from roots. You may not loose them this year, but you will eventually without protection unless with global warming our days of single-digit winters are over.